1. That I, just as much as any other sentient entity, deserve a modicum of compassion.
The analog code of the universe does not dictate that one person deserves less interpersonal fulfillment than another. When I had a massive fight with one of my dearest friends sophomore year, I feared no one else would ever come close to me again, which brings me to my next point--
2. A friend "breakup" may hurt as much or more than those of the romantic variety.
It's about as ubiquitous as adolescence to feel more secure in friendship than in something as grand and colloquial as love. While there is a considerable amount of discourse on "letting toxic people go" the end of an era always hurts and often alarms. Few high school students expect the boy with hair the color of kerosene to be in their lives forever,but your best friend is becomes constant as Sonata and Waltz combined.
3. Support can be found in a variety of places.
When my best friend and I topped talking, I thought I would feel the same level of complete isolation for the rest of my high school career. Chances are, you have more than one friend. I found a lot of love in people I had previously not spent as much time with. I still appreciate their patience with and compassion for me during that time. Don't be afraid to open up to someone you might not feel is "best friend' close to you. They might surprise you.
4. The sense of loss you feel will not linger as you fear.
I am not the only one who had a falling out with someone I thought would be in my life forever. You are not alone, not in gratitude or in grief, growth or retrograde.